We propose to characterize, on the molecular level, the interactions between integral membrane proteins and the cell cytoskeleton or matrix, with the objective of delineating the mechanisms which act to control mobilities in membranes. Our principal system for assaying matrix controls will be the spectrin-deficient spherocytic mouse erythrocyte (S-), a membrane system which lacks the major component of the peripheral matrix. To define the nature of matrix control, we will attempt the reconstitution of matrix function using erythrocyte membrane proteins, cytoplasmic proteins from other cells, and various non-protein polymers. Integral membrane proteins, and reconstituted matrices will be characterized by the determination of lateral diffusion coefficients by the technique of fluorescence redistribution after photobleaching and rotational diffusion coefficients from the kinetics of transient photo-induced dichroism. Proximity relationships within the matrix and of matrix components to the lipid bilayer surface will be derived from measurements of the efficiency of non-radiative transfer of excitation energy.